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Niobium (pronounced /naɪˈoʊbiəm/) (Greek mythology: Niobe, daughter of Tantalus), or columbium (/kəˈlʌmbiəm/), is the chemical element with the symbol Nb and the atomic number 41. A rare, soft, grey, ductile transition metal, niobium is found in the minerals pyrochlore, the main commercial source for niobium, and columbite.

Niobium has physical and chemical properties similar to those of the element tantalum, and the two are therefore difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical. The German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably. The name of the element was officially adopted as niobium in 1949.

It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although alloys contain only a maximum of 0.1%, that small percentage of Niobium improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet engines and rocket engines. Niobium is used in various superconducting materials. These superconducting alloys, also containing titanium and tin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, numismatics and jewellery. In the last two applications, niobium's low toxicity and ability to be coloured by anodisation are particular advantages.

Characteristics
Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table to right)
although it has an atypical configuration in its outermost electron shells compared to the rest of the members. (This can be observed in the neighborhood of niobium (41), ruthenium (44), rhodium (45), and palladium (46).)

The metal takes on a bluish tinge when exposed to air at room temperature for extended periods. Despite presenting a high melting point in elemental form (2,468 °C), it has a low density in comparison to other refractory metals. Furthermore, it is corrosion resistant, exhibits superconductivity properties, and forms dielectric oxide layers. These properties— especially the superconductivity —are strongly dependent on the purity of the niobium metal. When very pure, it is comparatively soft and ductile, but impurities make it harder.

The atoms of niobium is slightly less electropositive and smaller than the atoms of its predecessor in the periodic table, zirconium, while it is virtually identical in size to the heavier tantalum atoms as a consequence of the lanthanide contraction. As a result, niobium's chemical properties are very similar to the chemical properties of tantalum, which appears directly below niobium in the periodic table. Although its corrosion resistance is not as outstanding as that of tantalum, its lower price and greater availability make niobium attractive for less exact uses such as linings in chemical plants.

Occurrence
See also: Category:Niobium minerals
According to estimates, niobium is 33rd on the list of the most common elements in the Earth’s crust with 20 ppm. The abundance on Earth should be much greater, but the “missing” niobium may be located in the Earth’s core due to the metal's high density. The free element is not found in nature, but it does occur in minerals. Minerals that contain niobium often also contain tantalum, for example, columbite ((Fe,Mn)(Nb,Ta)2O6), columbite-tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6) and pyrochlore ((Na,Ca)2Nb2O6(OH,F)).\

Applications
A niobium foilIt is estimated that out of 44,500 metric tons of niobium mined in 2006, 90% ended up in the production of high-grade structural steel, followed by its use in superalloys. The use of niobium alloys for superconductors and in electronic components account only for a small share of the production.

Steel production
Niobium is an effective microalloying element for steel. Adding niobium to the steel causes the formation of niobium carbide and niobium nitride within the structure of the steel. These compounds improve the grain refining, retardation of recrystallization, and precipitation hardening of the steel. These effects in turn increase the toughness, strength, formability, and weldability of the microalloyed steel. Microalloyed stainless steels have a niobium content of less than 0.1%. It is an important alloy addition to high strength low alloy steels which are widely used as structural components in modern automobiles. These niobium containing alloys are strong and are often used in pipeline construction.

Superalloys
Apollo CSM with the dark rocket nozzle made from niobium-titanium alloyAppreciable amounts of the element, either in its pure form or in the form of high-purity ferroniobium and nickel niobium, are used in nickel-, cobalt-, and iron-base superalloys for such applications as jet engine components, gas turbines, rocket subassemblies, and heat resisting and combustion equipment. Niobium precipitates a hardening γ''-phase within the grain structure of the superalloy. The alloys contain up to 6.5% niobium. One example of a nickel-based niobium-containing superalloy is Inconel 718, which consists of roughly 50% nickel, 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum, 0.9% titanium, and 0.4% aluminium. These superalloys are used, for example, in advanced air frame systems such as those used in the Gemini program.

An alloy used for liquid rocket thruster nozzles, such as in the main engine of the Apollo Lunar Modules, is C103, which consists of 89% niobium, 10% hafnium and 1% titanium. Another niobium alloy was used for the nozzle of the Apollo Service Module. As niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle.

Superconducting magnets 
A 3 tesla clinical magnetic resonance imaging scanner using niobium-superconducting alloyNiobium becomes a superconductor when lowered to cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.2 K. Niobium has the largest magnetic penetration depth of any element. In addition, it is one of the three elemental Type II superconductors, along with vanadium and technetium. Niobium-tin and niobium-titanium alloys are used as wires for superconducting magnets capable of producing exceedingly strong magnetic fields. These superconducting magnets are used in magnetic resonance imaging and nuclear magnetic resonance instruments as well as in particle accelerators. For example, the Large Hadron Collider uses 600 metric tons of superconducting strands, while the International Thermonuclear Experimental Reactor is estimated to use 600 metric tonnes of Nb3Sn strands and 250 metric tonnes of NbTi strands. In 1992 alone, niobium-titanium wires were used to construct more than 1 billion US dollars worth of clinical magnetic resonance imaging systems.

 Columbite-tantalite minerals are most usually found as accessory minerals in pegmatite intrusions, and in alkaline intrusive rocks. Less common are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of niobium have been found associated with carbonatites (carbonate-silicate igneous rocks) and as a constituent of pyrochlore.

The two largest deposits of pyrochlore were found in the 1950s in Brazil and Canada, and both countries are still the major producers of niobium mineral concentrates. The largest deposit is hosted within a carbonatite intrusion at Araxá, Minas Gerais Brazil, owned by CBMM (Companhia Brasileira de Metalurgia e Mineração); the other deposit is located at Catalão, Goiás owned by Anglo American plc (through its subsidiary Mineração Catalão), also hosted within a carbonatite intrusion. Altogether these two Brazilian mines produce around 75% of world supply. The third largest producer of niobium is the carbonatite-hosted Niobec Mine, Saint-Honoré near Chicoutimi, Quebec owned by Iamgold Corporation Ltd, which produces around 7% of world supply.

Extensive though unexploited resources are located in Nigeria, Democratic Republic of Congo, Tanzania, Malawi, Australia and Russia.